The detection for being able to land on a tile when falling is slightly shifted to the left compared to the tile's normal hitbox detection. Because of this, when there is an open space under a vertical wall facing left, there is a specific point at the left edge of the wall at which you can jump straight up without getting obstructed, but which will cause you to then remain standing on a tile two tiles higher up on the straight wall. This way, it is possible to climb obstacles without needing the Jetpack. The trick only works when there are two cells of headspace above you; if you hit a ceiling, you fall down the entire way back to the real floor.